Communication system



March 12, 1940. R; F. DAWS 2,193,061

COMMUNICATION SYSTEM Filed Jan. 114, 1939 SPEAKER Our/ 0! Patented 1940 2,198,081 COMMUNICATION SYSTEM :PATENT' oFFlcs Robert F. Davis, Washington, D. 0. Application January 14, 1939, Serial No. 251,027

2 Claims. (01. 179-1) This invention relates to a system of communication particularly adapted for conversation between three or more stations, and so ar- "ranged as to afl'ord a'maximum degree of control of .the system at each of the stations.

Prior to this invention there were two systems of what is known as inter-oflice communica- 'tion in common use.

One of these systems includes a master unit which has complete control and a plurality of sub-station units which The other type 1 of system consists of a plurality of master staexercise no control whatever.

tion units, each of which possessesa certain amount of control over the system.

In the first mentioned system the master unit includes a loud speaker which acts also as a microphone, an amplifier, and certain switching mechanism which permits the operator to connect his unit to any one of the sub-station units in either one 01 two ways. If he wishes to talk to the sub-station, which sub-station consists merely of a loud speaker which will also act as a microphone, he connects the loud speaker at the master station to the input of the amplifier at that station and the output of the amplifierat that station to the loud speaker at the substation. -When he wishes to listen to someone at the sub-station he merely reverses the connection and is thus enabled to hear the signals which are picked up by the loud speaker at the sub-station," amplified, and reproduced by the loud speaker at the master station.

' 'mally connected to a loud In the other type of system in which all of the stations are of the master type, each unit has a pair of wires which constitute its normal or primary circuit, one-o1 which wires maybe a common or ground ,wire.

at that station. The operator at each of the other stations is then able to connect his loud speaker-microphone'into the input of his amplifler and connect his amplifier to the primary circuit er any other .stationtmwhich' he wishes to'speak; Having convened, it is necessary for him to break these and put his speaker back on its normal'for primary circuit, after which the operator atthe' station to'which he has spoken may reply by making the necessary connections, thatis, placing the loud speaker at the replying station in theinput circuit 01' the amplifier at the replying station and connecting the output of the amplifier at the replying which the replyis directed. 3

The use or the first arrangement described station to-the normal circuit of the station to These wires are norspeaker-microphone above involves a difliculty in that the sub-station operators can exercise no control over the system, cannot talk to the master station except when the master station is connected to listen to them and cannot talk to each other. The sec- 3 nd system has the disadvantage that it is necessary for the operator at a station that iscalled to be told the numberor name of the station calling him, and then, for this same operator to manipulate the switches on his box in order to reply. 11' it so happens that the electric power is turned 01! at the station that is being called, it then becomes impossible or the operator at that station to' reply until he has turned on the v electric current and allowed the vacuum tubes I l in the amplifier to become heated.

To overcome these diflicultles the present invention provides a system which may include all master station units, each of which can exercise a relatively complete control over the system, or may include with one "or more master station units. one or more sub-station units .which'can.

receive a message from any one of a plurality of master stations and can transmit a reply,-but which can exercise no control over the system. According to this invention an operator at any one of the master station 'units can initiate a conversation through any one of the stations to which he has a connection, whether it be a master station or a sub-station, and can carry one two-way'conversation with the operator at any one of these stations under his own complete control, without the necessity of. any action on the part of the operator at the called station, and regardless 01' whether or. not the electric power. at the called station is turned on. Since l w The present combines ,a feature which enables thejoperator of any ma erstation,

to ascertain whether or not the station to which he wishes to communicate is busy in anothercon: versation, and a ,feature which will. prevent eavesdroppins without preventing acall from be- 60 ing received should one he -made. a The new system comprises essentially a plurality oi stationaeach of which-includes a receiver: microphone and at least two .oi'which also in, clude an amplifier and certain switching devices.

, oi the amplifier.

receive a message A primary circuit is provided for eachv station in which the receiver-microphone of that station is normally connected and the switching devices are arranged so that at one position they disconnect the receiver-microphone at that station from its primary circuit and connect it to the input of the amplifier at the same station and at the same time connect the output of the amplifier to the primary circuit of any other selected station. This enables the operator to talk to any selected station. At another position this switching means connects the primary circuit of another station to the input of the amplifier at its own station, disconnects the receiver-microphone at its station from its normal primary circuit and connects this receiver-microphone to the output This enables the operator to from any selected station.

In addition to this mechanism, the system may also be provided with means operative to indicate the reception of the signal which will not act as a microphone and which is arranged to be connected into the primary circuit in lieu of the receiver-microphone of the particular station. This exchange need be made only when a confidential conversation is being carried on in the it may assume.

neighborhood of the station and it is desired that eavesdropping be prevented.

A consideration of the following description of one embodiment of the new system will furnish a detailed understanding thereof and an example of the principles involved therein. In connection with this description, reference should be had to the acompanying drawing in which:

Fig. 1 is a diagrammatic illustration of the preferred form of the system; and

Figs. 2 and 3 are diagrammatic illustrations of one of the switches showing positions that In the system illustrated in Fig. 1, there is shown diagrammatically two master stations A and B and a sub-station C. Each station has a receiver-microphone II which acts both to change electrical impulses into sound. and to change sound back into electrical impulses, depending upon the manner in which it is connected in the circuit. Station C consists only of the receiver-microphone, which is connected on one side to a ground and on the other to the normal 'or primary circuit l2 of that station. Each oi. the master stations Aand B includes in addition to thereceiver-microphone ii, an amplifier l3, a, talk-listen switch 14, which is shown in? Fig. 1 in its normal, or inactive position, and a selector switch i5 which is usedto select the station to which a connection is to be made. In addition there is provided at each of the master stations A and 'B an annunciator l6 or a receiver that will not act as a microphone, which can be used in lieu of the receiver-microphone I i to prevent "eavesdropping and yet announce the fact that the station. is being called. .This de- -viceis connected alternatively into the same circuit as is the receiver-microphone I! by means 7 wire will hereafter be referred to as the normal of,'-primary circuit i8 of station A and asthe normal of primarycircuit IQ of station BL As hasbeen stated. the talk lis'ten switch is shown as in its normal or inactive: position in tiate a conversation with the'operator at station B, and assuming that operation and his own his own amplifier is in switch I1 is connecting his own receiver-microphone ll into the circuit,

he need only perform the following operations.

First, he turns his selector switch l5 to the primary circuit I9 statton B. Next, he turns his talk-listen switch I to the talk position shown in Fig. 3, by which action the receiver-microphone li at station A is disconnected from its normal circuit l8 and inserted in the input circuit of the amplifier l3at station A and the output of the amplifier I3 is connected to the normal primary circuit IQ of station B, which in turn connects either to the receiver-microphone I I of that station or to the annunciator device iii of that station. If the connection is to the receivermicrophone of station B, the voice of the operator at station A will be heard when he speaks into his own receiver-microphone, and if the connection is to the annunciator l6, that device will operate either when the output of the amplifier of station A is connected to it or when the operator at station A speaks into his receiver-microphone. If the operator at station B has the annunciator i6 connected in lieu of his receiver-microphone; he must change the connection; .otherwise he need '-,do nothing but reply. When the operator aifstation A has com- 'mary circuit IQ of that station and the selector switch .l of station A and the talk-listen switch of that same station to the input of the amplifier atstation A, the output of which is connected through ceiver-microphone at station A. As the amplifier I3 at. station Bis not used in this process it is not even necessary that it be in operation during a conversation initiated and controlled by the operator at station A, If, however, the operator at station B wishes to initiate and con trol the conversation, he may do so in exactly the same manner as did the operator at station A but in that event it will be necessary that his the same talk-listen switch to the reamplifier be operating. The operatorat station and respond when he is called but is unable to initiate any calls or to control the conversation.

It will be obvious to those skilled. in the art that the form of the switches and particularly of the talk-listen switch may be ,varied according to individual taste and expediency and that the particular type of receiver-microphone, amplifier, or annunciator are not important insofar as the functioning of the system is concerned. It i s'only necessary that they be capable of performing the functions allotted to them. For example, the annunciator may be a loud speaker of a type that will not act as a microphone or it may be merely an annunciator that will not reproduce speech at all. The switch I! that connects this annunciator in the circuit may be biased so that it will normally tend to keep either the annunciator or the receiver-microphone in the circuit, whichever is preferred.

I claim:

1.- A system for intercommunication that comprises a plurality of stations each of which includes a receiver-microphone and at least two of'which also include an amplifier and switching means, and a primary circuit for each station in which the receiver-microphone of that station is normally connected, the switching means being arranged so as at one position to disconnect the receiver-microphone of its station from its primary circuit, connect the said station, and at another position to connect the primary circuit of another station to the input of the amplifier at its station, disconnect its receiver-microphone from itsprimary circuit and connect the said receiver-microphone to the output of said amplifier.

2. A system as described in claim 1 in which a. device that will indicate the reception of a signal but will not act as a microphone is arranged tobe connected in the primary circuit at at least one of said stations, in lieu of the receiver-microphone during periods when the station is not in active operation, so as to prevent eavesdropping but announce the fact when the station is called.

ROBERT F. DAVIS. 

